The correct answer to the question is : Gamma radiation.
EXPLANATION:
In a nuclear reactor, the water is heated due to the radiations coming from nuclear fission.
In the radioactive decay of uranium or other radio active substances, three types of radiations are produced which are known as alpha particle, beta particle and gamma ray.
Alpha particle is the double charged helium nucleus while beta is the stream of electrons. Hence, alpha and beta are the material particles. They are not radiations.
The gamma ray is an electromagnetic radiation. Hence, this will be responsible for heating water.
Hence, the correct answer is gamma radiations.
